1. Field of the Invention
The present invention relates to a tire mold for cure molding a tire, a manufacturing method of a pneumatic tire using the tire mold, and the pneumatic tire.
2. Description of the Related Art
In cure molding of a tire, an outer surface of an uncured tire is likely to be stuck to a tire molding surface of a tire mold, and an adhesive failure as shown in FIG. 6 may be generated by a rubber flow defect caused thereby. The adhesive failure is recognized as a region which is continuously peeled or depressed in a circumferential direction in the tire outer surface, and is remarkably generated particularly in a side wall portion. Further, such a rubber flow defect promotes an air residual between the tire molding surface and the tire outer surface, and causes a molding sink called a lightness or a bare generated on the outer surface of the cured tire.
In Japanese Unexamined Patent Publication No. H06-106921, there is described a pneumatic tire structured such that an outer surface of a side wall portion is partitioned into a plurality of fan-shaped regions which are adjacent in a circumferential direction, and a difference of surface roughness is made equal to or more than 50 μm between the adjacent fan-shaped regions, for making inconspicuous a stripe-like irregularity trace generated by a joint portion of a carcass ply. Further, the publication No. H06-106921 describes changing a surface roughness of a tire molding surface of a tire mold for molding such a tire, and it is considered to be possible to improve a flow property of the rubber by suppressing an adhesion of an uncured tire at the time of cure molding, as far as the surface roughness corresponding to the fan-shaped region is rough.
However, in the tire mold mentioned above, since a micro convex portion included in the region in which the surface roughness is rough forms a micro concave portion which is deep and sharp to the tire side, a strain tends to be concentrated to the portion, and there is a problem that it becomes a starting point of the crack on the tire outer surface. However, if the surface roughness of the region is lowered, it has an effect on prevention of a crack, however, since a flow resistance of the uncured rubber with respect to the tire molding surface is increased, a rubber flow defect is generated at the time of the cure molding and an appearance fault such as an adhesive failure or the like is generated. As mentioned above, with regard to the surface roughness of the tire molding surface, it has been difficult to secure the flow property of the rubber and to prevent the crack on the tire outer surface at the same time.